A conventional monitoring system displays a plurality of monitoring images photographed by a plurality of monitoring cameras on a plurality of image display devices or displays the monitoring images on a single image display device by division, thereby performing monitoring. Alternatively, a plurality of monitoring images is switched by time division and is displayed on a single image display device, thereby performing monitoring. However, the conventional monitoring system is not suitable for the case in which an inner part of a building having a complicated structure is monitored.
In other words, a large-scaled building such as a factory or a building has a complicated floor structure and a large number of rooms. In order to monitor an inner part of the building having the complicated structure, a large number of cameras are provided so that the number of monitoring images to be displayed on an image display device is also increased. For this reason, it is hard to grasp, at a glance, which floor and which room for a plurality of monitoring images displayed on the image display device and it is difficult to understand a situation of the whole building.
In contrast, there is proposed a system for synthesizing monitoring images photographed by monitoring cameras provided for each of monitoring regions of a floor with another prepared floor image, thereby enabling the monitoring images to be displayed on a single screen at a time in accordance with a layout of the floor (for example, see Patent Document 1). According to the technique described in the Patent Document 1, it is possible to simultaneously monitor monitoring regions such as an inner part of each room, a corridor or the like in a building through a single screen in accordance with a layout of a floor.
Referring to the technique described in the Patent Document 1, however, the monitoring images photographed by the monitoring cameras provided in respective monitoring regions are simply allocated and displayed in positions of the monitoring regions for a planar floor image shown in a top view. Accordingly, this is basically the same as division and display of a plurality of monitoring images on a single image display device to perform monitoring. Therefore, it is possible to grasp which monitoring region has the monitoring images photographed. However, there is a problem in that it is necessary to individually confirm the monitoring images in order to understand a situation of a whole building and it is still hard for a user to use them.
Moreover, the technique described in the Patent Document 1 is not suitable for monitoring a building having a large scale and a complicated floor structure. In other words, the technique of the Patent Document 1 serves to divide and display the monitoring images on a single screen. For this reason, the number of images which can be displayed has a limit. As shown in FIG. 7 of the Patent Document 1, really, the monitoring images photographed in the monitoring regions in one floor can be simply displayed and cannot be used for wholly monitoring a large-scaled and complicated building such as a factory, a building or a department store. If a large number of monitoring images are to be forcibly displayed on a single screen, display sizes of the individual monitoring images are reduced so that they are hard to see.
According to FIG. 9 in Japanese Laid-Open Patent Publication No. 2008-118466 (Patent Document 2) cited as the prior art document in paragraph [0004] of the Patent Document 1, monitoring images in a plurality of rooms are synthetized to generate an overlooking image every floor (such an image as to look at each floor downward) and overlooking images in the floors are further synthesized to generate floor superposition images 1F to 3F. Consequently, a whole monitoring image of a building having a plurality of floors or the like can be displayed on a single screen.
When a whole monitoring image of a large-scaled and complicated building is to be thus displayed on the single screen, however, display sizes of the monitoring images in the individual monitoring regions are reduced so that the monitoring images are very hard to see. Accordingly, it is also difficult to say that the technique described in the Patent Document 2 is suitable for monitoring a building having a large scale and a complicated floor structure.
Patent Document 1: Japanese Laid-Open Patent Publication No. 2012-4630
Patent Document 2: Japanese Laid-Open Patent Publication No. 2008-118466